The aim of this paper is to present methods for corrosion mitigation in molten salt environments. The corrosion of structural materials depends directly on the redox potential of the salt. When the redox potential of the salt is higher than the standard potentials of the elements constituting the structural materials, corrosion occurs. If the reverse is true, no corrosion is observed. Herein, a methodology for calculating the theoretical potential of a molten salt is provided and compared with experimental measurements. Three ways to mitigate corrosion by modifying the salt redox potential are proposed: (i) using a soluble/soluble redox system; (ii) using a potentiostatic method; and (iii) using an amphoteric compound such as UCl₃, TiCl₂, or TiCl₃. Immersion tests were conducted under the above conditions to validate the methodology.

An alkaline etched, superhydrophilic aluminum surface was modified using functionalized alkyl compounds selected to study the effect of their properties on adsorption on the metal surface. The thirteen organic compounds differed in alkyl chain length (eight and eighteen carbon atoms) and anchor group (azide, imidazole, thiocyanate, amino, disulfide, thiol, phosphonic, carboxylic, and benzoic). The methodology of the study integrated a complete chain of steps incorporating synthesis, electrochemical and surface analyses, and computational modeling. The corrosion resistant and superhydrophobic properties depend on the anchor group, which governs adhesion to the surface, and backbone, which is responsible for lateral cohesive interactions. The morphology and chemical composition of modified layers were studied using scanning electron microscopy, X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Electrochemical and long-term immersion properties were investigated in 0.5 M NaCl. Calculations based on density functional theory were performed as to model the adsorption of selected anchor groups on the hydroxylated oxidized aluminum surface. Integrated results allowed the identification of the anchor groups that are able to form inhibitive adsorbed layers on Al surface regardless the alkyl chain length, and those that are not able to form adsorbed layers at all and are thus not efficient corrosion inhibitors.

The ability of surfactant-like compounds to inhibit the corrosion of aluminum in NaCl solution was systematically investigated. The basic idea of this study was to scrutinize the effect of type of backbone chain (alkyl and perfluoroalkyl), length of backbone chain (number of carbon atoms 7, 10, and 17), various anchor groups (carboxylic, thiol, and imidazole) and presence of alkylene and benzene spacers between perfluoroalkyl chain and anchor group. To tackle these effects, three model studies were designed for alkaline etched, superhydrophilic aluminum surface and then approached experimentally and by density functional theory modeling. This enabled us to decouple the adsorption affinity of selected anchor groups on the hydroxylated aluminum surface from the lateral intermolecular cohesive interactions between hydrophobic backbone chains. Fourteen compounds were used to study the changes in the surface composition, wettability and the electrochemical barrier properties. For the carboxylic anchor group, the length and type of chain are important for barrier properties and also for tuning the wettability of the surface. The addition of alkylene spacer to perfluoroalkyl chain significantly affects the properties of the modified surface. Thiol and imidazole anchor groups, however, are not efficient inhibitors regardless the type and length of backbone chains.

A carbon steel container including nuclear glass has been altered for 2 years in Andra’s Underground Research Laboratory to simulate the behaviour of waste package. Post-mortem analyses at different scales (macro–micro–nano) have been performed to identify neoformed phases on iron corrosion products (ICP) and in the glass alteration layer (GAL). It has been shown at nanometric scale that important quantities of iron and silicon were found in the GAL and in the ICP respectively. Using a comparative approach with phyllosilicate references, STXM, at Si-K edge, suggests presence of trioctahedral species in the GAL and in ICP. Relevant fits of the STXM spectra are obtained with a Fe-rich chlorite for the nanostructured GAL, which could be formed according to chloritisation mechanism. This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.